Study On Pathogen Identification, Field Occurrence Dynamic And Chemical Control Of Shortbody Nematodes Disease On Dioscorea Opposita Thunb.

Shortbody Nematodes Disease on D.opposita Thunb. is a kind of seriously increasing soil-borne disease which badly restrict production. However, relevant research reports are few. In this paper, species identification and soil occurrence dynamics were studied, and nematocides with high efficiency, low toxicity were carried out, aiming to provide theoretical foundation to integrated control. Results are as follow:1. Pathogen of nematode disease on D. opposita Thunb.was identified through morp Hology observation and PCR amplification sequencing, the result showed: pathogen of nematode disease on D. opposita Thunb. was P. coffeae.2. Occurrence dynamics of soil nematodes. Using five-point-sampling mode, to sample from 0~20cm, 21~40cm, 41~60cm and 61~80cm soil layers respectively. Isolating and counting the population of living nematodes through shallow dish method and sieving method. The results showed that most nematodes were located in 0~40cm soil layer and the density of nematodes were decreased with increasing depth. Population of soil nematodes were influences by the growth period of yam. Nematodes in 0~40cm soil layer increased along with the growing yam tuber, especially in the tuber’s rapid growth period(July). However, there are no significant change in 41~80cm soil layer.3. Indoor toxicity test. Indoor screening of 11 pesticides against P. coffeae were investigated using contacting method. The results showed that effect of 35% metham-sodium and5%f osthiazate are higher than the other 9 pesticides significantly. After 72 h disposing, corrected mortality of 35% metham-sodium diluted 200 times higher than 5% fosthiazate diluted 200 times at 84.57% significantly,followed by other 9 pesticides which was lower than 30%. It’s obvious that 35% metham-sodium is the most effective. The LC50 and LC90 of metham-sodium and fosthiazateagainst P. coffeae were tested in laboratory. The result showed: both LC50 and LC90 of this two nematicides are decreased along with time. The LC50 and LC90 values of metham-sodium at 48 h were 0.263 and 1.601 g/kg respectively, and of fosthiazate at 48 h were 0.226 and 1.432 g/kg respectively. Accordingly, fosthiazate has better efficiency than metham-sodium with the same effective concentration.4. Field efficiency experiment. Protecting efficiency of 3 pesticides against soil nematodes were carried out through isolating nematodes from soil and counting its population. The result showed: 10.5% abamectin?fosthiazate, 42% metham-sodium and 99.5% chloropicrin all had preferable effects on controlling soil nematodes, and morality of the 3 pesticides were more than 60% respectively, but there is no difference among the three, and efficiency of all the 3 pesticides were higher than CK, significantly. At the same time, the efficiency of the 3 pesticides agaisnt P. coffeae were investigated. The results showed that three pesticides had preferable effects on controlling shortbody nematode disease and increased production; the average control effects and the average increasing rates of two pesticides that 42% metham-sodium and 99.5% chloropicrin were 91.75%, 77.37%, 602.00% and 601.79% respectively; the control effects and the increasing rates of 10.5% abamectin?fosthiazate were 87.48% and 537.29% respectively.